Insect infestations and the damage they cause are as old as human history. One of the seven plagues visited on Egypt by God in the Old Testament is a locust infestation. An unchecked insect pest, such as a fruit fly, can destroy an entire agricultural industry in an area The whole face of the south was changed in the early part of the twentieth century by the boll weevil and its impact on cotton farming.
Because of natural predators, many insects will try to remain hidden. Detection by ordinary as visual means may be difficult, if not impossible. Therefore, for imported food or other natural materials, quarantines of the imported material are sometimes required or even irradiation or sterilization.
Like all other animals, insects inspire oxygen and respire carbon dioxide (CO.sub.2). However, CO.sub.2 gas is present in the atmosphere in large quantities, Therefore, the quantity of CO.sub.2 produced by an individual insect is difficult to detect in the presence of naturally occurring CO.sub.2 because of the variations that are normal within a CO.sub.2 concentration in a particular area Not only insects produce CO.sub.2, but internal combustion engines, other animals, and other chemical operations that use carbon may also produce CO.sub.2. Therefore, even fairly substantial infestations of insects do not ordinarily produce enough CO.sub.2 to make detection possible. While it may be possible to use a slow long-term test that establishes a base line, this is not effective for most applications.
Consequently, it has been recognized that it can be useful to use infrared carbon dioxide gas analysis to detect hidden insect infestations. Two systems have been proposed to use infrared analysis of carbon dioxide to detect hidden insect infestations. In Bruce et al., U.S. Pat. No. 3,963,927, a system for detecting respired CO.sub.2 is disclosed. Here, a sample of the materials in which an insect infestation is suspected is sealed in a chamber. The air inside the chamber is held stable for an interval of time then moves through the system as a plug flow or bolus through an infrared analyzer. The sample chamber in which the material to be tested is placed is first purged with a carrier gas and then sealed off for a long enough time to allow respired CO.sub.2 by insects contained within the sample material to build up and reach a concentration sufficient for detection. It is this gas which is analyzed for higher CO.sub.2 concentration and compared to the earlier carrier baseline gas.
Delgrosso, U.S. Pat. No. 4,206,353, also discloses a system for detecting live insects in a commodity. This invention, like the Bruce et al Patent, uses a closed chamber with an incubation time and a purge by a base line or reference gas. Outside air is used as a reference to compare against air from within the closed chamber where the presumed sample has incubated, hence, allowing any insects contained within the sample to respire sufficient carbon dioxide within that sample for detection by an infrared detection device.
These devices, while useful, especially for commodity products like wheat or rice that can be easily sampled, cannot be used to detect insects in many applications where detection is important. These devices require a sealed chamber as part of the device to allow a controlled increase in the CO.sub.2 concentration in the chamber for detection. This means the product where an insect infestation is suspected must be like wheat or rice that are easily sampled for testing in a sealed chamber.